not a 500, but big bore and long stroke

[AlisoBob]

For quite a while, exposed valvetrains were commonplace in aircraft engines. The mechanic would oil up everything before take off, and off ya' go.......

As for the rod bearing issue.... the rods are not lubricated by "oil pressure" as most people think.

Oil gets pumped into the crankshaft, and centrifugal force takes it from there.

You might have 50 psi at the mains, and the equivalent of 120psi at the rods at high rpm due to centrifugal force.

The rod bearing in the CR500 is the hardest thing to lube... as oil is constantly being flung off of it...

[dannygraves]

if there isn't enough pressure to get to the valvetrain, then there isn't enough to come out an oil sprayer, the oil sprayers have a little ball and spring assembly to only allow them to spray at over a set psi (mitsubishi is 20psi, for their turbo motors that have sprayers)

[M.F.D.B.]

There is no such thing in the sprayers on any dirt bike ive ever worked on. Its basically the same plumbing as a leak jet setup on the accelerator pump. According to physics, fluids always take the path of least resistance which means most of that tiny amount of oil thats left gets pumped right back where it started via the squirter. Im guessing since most thumpers have roller rod bearings that any type of spring/bearing setup would just cause too much oil to be diverted through the rod bearing instead of "squirted" onto the piston?

[Roostius_Maximus]

a drysump stil has to scavenge the oil, if theres a hole in any part of the engine it will draw from the easiest source. like trying to suck chocolate milk up a straw with a hole.
In our stock car engines we run so much negative pressure we have a regulator to vent atmosphere into the crankcase. we run enough vaccum to seal the rings tighter, but trim it so it wont suck the crank seals or gaskets in. We also have to run a pop-off so when my guy comes into the corner at 9800 and stuffs the brake the engine drops about 4000 rpm and goes into positive pressure.

[M.F.D.B.]

Roosty, on the Yami thumper I own, they have seperate scavenge and pressure sides. The scavenge pulls from the bottom of the case and pumps to the oil resevoir only. Then the pressure takes it where it needs to go. On the Hondas, they are wet sump, so a short cicuit is just as bad...

[hoofarted]

Interesting thread...

[Roostius_Maximus]

ya, same thing like we use, 3 sections of scavage and 1 section of pressure. common for us is the scp-204-a
http://pumps.scpdrysumps.com/

routed something like this....



we'll usually mount the krc power steering pump on the back of it, and sometimes spud an enderle fuel pump to that yet too

[M.F.D.B.]

That drawing is hilarious! It depicts a motor with huge velocity stacks and dry sump (exotic) oiling and then they put some stock looking exhaust "manifolds"...HAHAHA

[Roostius_Maximus]

ya,

[dannygraves]